One of the problems with riding an older, unusual motorcycle is that parts can be difficult to find. I've already had to carefully repair and refurbish a broken mirror for my Honda PC800 to replace a completely destroyed one since intact ones are so rare and prices so high. My tires are a little worse for wear, and I need to replace them before the spring riding season begins. We've written about how to choose new motorcycle tires before. Unfortunately, it uses tires of unusual size (not to be confused with Rodents Of Unusual Size), which has made tire shopping rather difficult.
The PC800 originally came with Dunlop K177 tires. This model was later replaced by the K555, which is still made today. These tires are okay, but riders report a tendency for the tire to wander as it goes down the road. Metzeler offers an alternative with the ME880, which are what my bike came with and I've used ever since. These are also okay, but not wonderful, and tend to moan in the turns even when you're not pushing very hard. Yet these two models are the only ones that have both front and rear tires available in the original sizes.
Fortunately, we have the internet. The Honda Pacific Coast Facebook group is full of knowledgeable people from all over the world about this unusual bike, as is the old Internet Pacific Coast Riders Club Yahoo group. Douglas Van Bossuyt also has extensive PC800 links and knowledge on his website, including a page dedicated to the PC800 tire situation. Clark Rice, another member of the Facebook group, also shared with me a spreadsheet he's compiled of available tires equal or close the PC800's stock sizes.
On my cars I've often strayed from the manufacturer recommended tire size. It's common practice to get narrower, taller snow tires, and wider, shorter summer tires. I have to watch out for somewhat tight clearance issues, between the swingarm and the huge trunk that surrounds the back tire. Fortunately, having a late PC800, I have a standard front fender, not the giant skirt surrounding the front wheel like a Goldwing or BMW K1, which may let me get away with a little more flexibility.
My Honda Shadow ACE 1100 came with fairly new Michelin Commander 2 tires. I love them. Even though a sport touring bike is supposed to handle better than a cruiser, my Shadow has always felt more planted and connected to the road than my PC. After referring to all of these online resources, it looks like I may be able to use these tires on my PC if I change the sizes up a little. I'll need a slightly wider 130/80-17 instead of a 120/80-17 for the front, and a slightly shorter 140/75-15 instead of 140/80-15 for the back. The problem with that is the rear is a radial tire while the front would be bias ply, two types that you shouldn't mix unless the manufacturer specifies it. Upsizing to a 140/90-15 would get me a bias ply tire, but risk touching the trunk or swingarm.
I could just get yet another pair of mediocre Metzelers that I know will work. I think I might try the Michelins, though. They're slightly less money, and my experience with them on my Shadow is making me want them for my PC as well. Other PC riders seem to have made them work, so I just might, too.
It's a wonderful time to be a weird old bike enthusiast. No matter what the model, there's an internet group of some kind for it and people there who know a lot more than you do, no matter how much you think you know. You also need to think outside the box sometimes—or, in this case, outside the original tire size.